Phaeochromocytoma

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Phaeochromocytoma

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A phaeochromocytoma is a rare tumour that secretes catecholamines. It is derived from chromaffin cells, usually in the adrenal medulla; however, occasionally extra-adrenal phaeochromocytomas or paragangliomas occur[1]. Many - but not all - authors define phaeochromocytoma as coming from the adrenal medulla and if the tumour is similar but located elsewhere, it is called a paraganglioma.

The excessive production of catecholamines may cause life-threatening hypertension or cardiac arrhythmias. If the diagnosis is overlooked, the result can be disastrous or fatal but, if this rare tumour is diagnosed, it is curable.

Up to one third of all symptomatic presentations of phaeochromocytoma or paraganglioma are due to germline mutations in one of six genes defining multiple endocrine neoplasia type 2, von Hippel-Lindau (VHL) disease, neurofibromatosis type 1 and the paraganglioma syndromes types 1, 3 and 4[2].

Background

The name is of Greek etymology. Phios means dusky, chroma means colour and cytoma means tumour. This refers to the colour of tumour cells when stained with chromium salts.

A normal adrenal medulla secretes in response to neural control and produces about 85% adrenaline (epinephrine) whereas the tumours are not innervated and the stimulus for secretion is unknown. They may secrete constantly or intermittently. The familial type tends to produce mostly noradrenaline (norepinephrine) but the sporadic type produces mostly adrenaline (epinephrine). Dopamine may also be produced.

Epidemiology

They occur in between 0.5 and 2 in 1,000 patients with hypertension but patients may be normotensive or have a labile blood pressure.

10-15% of phaeochromocytomas are malignant, 18% extra-adrenal and 20% familial[3].

Often, the diagnosis is made at autopsy.

There is no sex difference in incidence or any particular racial predisposition.

Diagnosis is usually made between the third and the fifth decades.

Approximately 10% occur in children.

In children, 50% are solitary adrenal tumours, 25% are bilateral and 25% are extra-adrenal. They are more likely to be familial than those presenting in adults[4].

Inherited forms

Phaeochromocytomas occur in certain familial syndromes, including:

Multiple endocrine neoplasia (MEN) syndrome.

Neurofibromatosis.

Von Hippel-LIndau (VHL) disease.

It was thought that 10% of cases represent inherited syndromes but this figure may be up to 30%[5].

Investigations

Blood tests

Blood glucose is often raised.

Calcium may be elevated.

Haemoglobin is elevated due to haemoconcentration from reduction in circulating volume.

Plasma catecholamines and plasma metanephrines (the o-methylated metabolites of catecholamines) have both been used in diagnosis[7]. A recent consensus guideline stated that plasma free metanephrines were the blood test of choice[8].

Urine

The bottle for collection should be dark and acidified and should be kept cold to avoid degradation of the catecholamines.

Preferably collect urine immediately after a crisis.

Physical stress and a number of drugs may interfere with the assay and cause false elevation of metanephrines. Drugs include tricyclic antidepressants, alcohol, levodopa, labetalol, sotalol, amfetamines, benzodiazepines and chlorpromazine.

Urinary VMA has a false positive rate in excess of 15%. One study found that of all urine and blood tests, urine free metanephrines produced the best results[7].

Imaging

After biochemical confirmation of a tumour, imaging is necessary to locate it[9].

Extra-adrenal phaeochromocytomas develop in chromaffin tissue of the sympathetic nervous system and can occur anywhere from the base of the brain to the urinary bladder.

Common locations for extra-adrenal phaeochromocytomas include close to the origin of the inferior mesenteric artery, bladder wall, heart, mediastinum and carotid and glomus jugulare tumours.

Various techniques may be employed:

CT is the initial imaging modality of choice - it is sensitive and detects around 85-95% of tumours in excess of 1 cm in diameter.

If phaeochromocytoma is confirmed biochemically but CT or MRI do not show a tumour, a scan with metaiodobenzylguanidine (MIBG) labelled with 131 iodine or 123 iodine may be performed[10]. The molecular structure of MIBG is similar to noradrenaline (norepinephrine) and concentrates within adrenal or extra-adrenal phaeochromocytomas.

A somatostatin receptor analogue called pentetreotide, labelled with 111 indium is less sensitive than MIBG but may be used to detect phaeochromocytomas that do not concentrate MIBG[4].

Positron emission tomography (PET) scanning appears promising but is still in fairly early stages of assessment[11].

Genetic testing

All patients should be involved in shared decision-making for genetic testing[8]. Tumour location and number, age, gender and family history will point to the need for genetic testing. Such testing forms the basis of early diagnosis and follow-up including management of relatives[2].

Histology

Histological assessment of tissue removed after surgery using certain criteria (the PASS system) can help to differentiate benign from malignant tumours. A PASS score of <4 is predictive of benign phaeochromocytomas, whereas a score greater than 6 is characteristic of malignant tumours. Such patients should be followed closely for recurrence[12].

Risk factors

Any of the following may precipitate a hypertensive crisis:

Induction of anaesthesia.

Opiates.

Dopamine antagonists.

Decongestants such as pseudoephedrine.

Drugs that inhibit the reuptake of catecholamines, including tricyclic antidepressants and cocaine.

X-ray contrast media.

Childbirth.

Differential diagnosis

If the urine tests for total catecholamines, VMA and metanephrines are positive, the main differential diagnosis is to decide if is it is part of a familial condition.

Management

Associated conditions must be sought and, if found, appropriate management includes genetic counselling.

Surgical resection of the tumour is the treatment of choice and usually results in cure of the hypertension. Pre-operative treatment with alpha-blockers and beta-blockers is required to control blood pressure and prevent intraoperative hypertensive crises.

Alpha blockade with phenoxybenzamine is started at least 7 to 10 days before operation to allow for expansion of blood volume.

Only once this is achieved is beta blockade considered. If beta blockade is started too soon, unopposed alpha stimulation can precipitate a hypertensive crisis.

Complete resection of the tumour is usually possible and surgical mortality rates are less than 2% or 3% with an experienced anaesthetist and surgeon.

Laparoscopic surgery is being used more often for tumours smaller than 6 cm but for larger tumours, an open operation is probably safer[14].

After surgery, a 24-hour urine collection for total catecholamines, metanephrines and VMA is required two weeks after operation. If results are normal, the prognosis is excellent. It is important to ensure that hypertension is controlled or resolved. Lifelong annual biochemical testing is recommended to detect recurrent or metastatic disease[8].

Sometimes, when a patient is being investigated for hypertension, a mass may be found in an adrenal gland. This may represent phaeochromocytoma, glucocorticoid excess or primary aldosteronism. The mass may even be irrelevant and misleading. Such findings are called 'incidentalomas'. If the clinical history or physical examination of a patient with unilateral incidentaloma suggests glucocorticoid, mineralocorticoid, adrenal sex hormone or catecholamine excess, which is confirmed biochemically, the treatment of choice is often adrenalectomy[15]. In one study of 201 patients with incidentalomas, 30% were found to have a phaeochromocytoma[16].

In the rare malignant cases, palliative care may be achieved with radiotherapy and chemotherapy. New emerging therapies, such as the tyrosine kinase inhibitor sunitinib, which rectifies the results of genetic abnormalities, may revolutionise the treatment of malignancy in the future[17].

Prognosis

The five-year survival rate for non-malignant phaeochromocytoma is over 95% but for malignant phaeochromocytomas it is less than 50%. The risk of malignancy is rather higher when children are affected[18].

Most paragangliomas arise from chromaffin tissue, along the para-aortic sympathetic chain, or within the organs of Zuckerkandl at the origin of the inferior mesenteric artery, the wall of the urinary bladder and the sympathetic chain in the neck or mediastinum. They are usually benign and amenable to surgical resection. Around half are hereditary and so genetic testing should be considered[19]. They can recur many years after initial presentation, so long-term follow-up is important[1].

Phaeochromocytoma and pregnancy

Pre-eclampsia is fairly common, whilst phaeochromocytoma is very rare and only a few hundred cases in pregnancy have been reported in the literature.

If phaeochromocytoma is diagnosed for the first time in pregnancy, there are special concerns with a maternal and fetal mortality rate of 48% and 55% respectively.

If diagnosis precedes pregnancy, the outcome is vastly better. Alpha-adrenergic blockade with phenoxybenzamine is required as soon as the diagnosis is made.

If surgery is performed in the first or second trimester, the pregnancy need not be terminated but fetal loss is high.

In the third trimester, as soon as fetal lung maturity is confirmed, lower segment caesarean section (LSCS) followed by surgical removal of the tumour are required[20].

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